1. Field of the Invention
The present invention relates to a curing epoxy resin composition which permits water-repellent and ink-repellent surface treatment. Particularly, the present invention relates to an epoxy resin composition capable of forming a film pattern by ultraviolet irradiation, a surface treatment method using the resin composition, a liquid-jet recording head subjected to ink-repellent treatment with the epoxy resin composition, and a liquid-jet recording apparatus using the liquid-jet recording head.
2. Description of the Related Art
In various fields, a method of applying a water-repellent coating to a member required to have water resistance and ink repellency to obtain these properties is generally known, and resin materials and coating materials used for the method have been developed. For example, films of fluoropolyolefin and a fluororesin coating material having perfluoro groups are thermally and chemically stable, excellent in weather resistance, water resistance, chemical resistance, solvent resistance, etc., and further excellent in release property, abrasion resistance and water repellency; such films are widely used for various applications.
Meanwhile, a liquid-jet recording head adapted to discharge liquid droplets such as ink droplets through discharge nozzles and cause them to adhere to a recording medium such as a sheet of paper so as to record or form an image thereon has only recently been required to be able to discharge smaller liquid droplets, be driven with a higher driving frequency, and have a larger number of nozzles in order to improve recording properties. Therefore, a treatment for maintaining the nozzle surface in a clear state becomes more important. However, it is difficult to selectively treat the surface of a nozzle or precisely treat the surface in the form of a pattern using any existing material which avoids ink adhesion. This is because first, a material mainly comprising a compound having a photosensitive functional group must be used as a surface treatment material for treating the surface in the form of a pattern so that the material has characteristics like photoresist suitable for pattern treatment; however, it is very difficult to design the molecule of such a compound so that the compound has water repellency and ink repellency at the same time.
Second, if the nozzle surface can be treated with an existing fluorocarbon material, a film structure must be designed so as to maintain the properties of the surface for a long period of time. A material permitting such a pattern surface treatment having the above-described properties is extremely valuable for surface treatment of an ink-jet print head, as described below.
Namely, in an ink-jet recording system in which an ink is ejected as droplets, the discharge orifice (nozzle) is preferably designed to have the following characteristics:
(1) The residual ink of ink columns having turned into droplets is immediately held back into the nozzle.
(2) The ink droplets adhering to the nozzle surface can be readily wiped off by a cleaning operation.
(3) The nozzle surface has excellent scratch resistance against the cleaning operation and paper transfer.
(4) In repeated formation of droplets and ink refilling, a meniscus is formed on the nozzle surface (refer to reference numeral 23 in FIG. 1).
(5) The discharge direction is normal to the meniscus.
(6) Even with an ink having low surface tension or under low-negative pressure, the interfacial tension, i.e., the contact angle, is sufficient to form the meniscus.
The above-noted characteristics are required for the discharge orifice because if a recording liquid such as an ink adheres to the periphery of the orifice, the discharge (flying) direction of the ink droplets discharged from the orifice deviates, making it impossible to print highly accurately and directly degrade the printing performance. In order to prevent adhesion of the ink to the vicinity of the discharge orifice, which causes a deviation in the discharge direction, a method is known in which the surface of the discharge orifice is subjected to water-repellent treatment.
For example, a method of ink-repellent treatment with a polymer having fluoroacetyl groups and silazane groups is known as prior art relating to the above-described surface treatment (for example, Japanese Patent Laid-Open No. 2-39944). On the other hand, as a result of the increasing demand for sophisticated printers utilizing liquid-jet recording systems for recording images, the recording liquid to be used for such recording systems is also required to show sophisticated characteristics. More often, the recording liquid to be used for such recording systems is chemically regulated to be basic with a pH value of 7 to 11 in order to further improve dissolution stability and dispersion stability of contents, and thus a structural material highly resistant against alkali and hydrolysis must be used for a printer member.
However, when a recording liquid containing a polar organic solvent or a recording liquid showing such a high pH value is used, a water-repellent agent applied for treating the surface of the discharge orifice in order to satisfy the above requirements can damage the film forming property of the agent and the tight adhesion of the agent to the surface of the discharge orifice as it comes into contact with the solvent of the recording liquid, particularly the polar organic solvent of the recording liquid. Then, the coat of the water-repellent agent can be peeled off to decrease the water repellency of the surface.